<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=2">
<meta name="theme-color" content="#222">
<meta name="generator" content="Hexo 5.4.0">
  <link rel="apple-touch-icon" sizes="180x180" href="/images/Frog_32px_1177822_easyicon.net.ico">
  <link rel="icon" type="image/png" sizes="32x32" href="/images/Frog_32px_1177822_easyicon.net.ico">
  <link rel="icon" type="image/png" sizes="16x16" href="/images/Frog_16px_1177822_easyicon.net.ico">
  <link rel="mask-icon" href="/images/Frog_32px_1177822_easyicon.net.ico" color="#222">

<link rel="stylesheet" href="/css/main.css">


<link rel="stylesheet" href="/lib/font-awesome/css/all.min.css">
  <link rel="stylesheet" href="/lib/pace/pace-theme-minimal.min.css">
  <script src="/lib/pace/pace.min.js"></script>

<script id="hexo-configurations">
    var NexT = window.NexT || {};
    var CONFIG = {"hostname":"hxy1997.xyz","root":"/","scheme":"Pisces","version":"7.8.0","exturl":false,"sidebar":{"position":"left","padding":18,"offset":12,"onmobile":false},"copycode":{"enable":false,"show_result":false,"style":null},"back2top":{"enable":true,"sidebar":false,"scrollpercent":false},"bookmark":{"enable":false,"color":"#222","save":"auto"},"fancybox":false,"mediumzoom":false,"lazyload":true,"pangu":false,"comments":{"style":"tabs","active":"valine","storage":true,"lazyload":true,"nav":null,"activeClass":"valine"},"algolia":{"hits":{"per_page":10},"labels":{"input_placeholder":"输入关键字","hits_empty":"没有找到与「${query}」相关搜索","hits_stats":"${hits} 条相关记录，共耗时 ${time} ms"}},"localsearch":{"enable":true,"trigger":"auto","top_n_per_article":1,"unescape":false,"preload":false},"motion":{"enable":true,"async":false,"transition":{"post_block":"fadeIn","post_header":"slideDownIn","post_body":"slideDownIn","coll_header":"slideLeftIn","sidebar":"slideUpIn"}},"path":"search.json"};
  </script>

  <meta name="description" content="有点意思，转自TypeScript 中类型 any，void，unknown，never之间的区别">
<meta property="og:type" content="article">
<meta property="og:title" content="TypeScript 中类型 any，void，unknown，never之间的区别">
<meta property="og:url" content="https://hxy1997.xyz/2021/08/22/TypeScript%20%E4%B8%AD%E7%B1%BB%E5%9E%8B%20any%EF%BC%8Cvoid%EF%BC%8Cunknown%EF%BC%8Cnever%E4%B9%8B%E9%97%B4%E7%9A%84%E5%8C%BA%E5%88%AB/index.html">
<meta property="og:site_name" content="hxy的博客">
<meta property="og:description" content="有点意思，转自TypeScript 中类型 any，void，unknown，never之间的区别">
<meta property="og:locale" content="zh_CN">
<meta property="article:published_time" content="2021-08-21T16:00:00.000Z">
<meta property="article:modified_time" content="2021-08-21T16:03:06.329Z">
<meta property="article:author" content="hxy">
<meta property="article:tag" content="TypeScript">
<meta property="article:tag" content="类型">
<meta name="twitter:card" content="summary">

<link rel="canonical" href="https://hxy1997.xyz/2021/08/22/TypeScript%20%E4%B8%AD%E7%B1%BB%E5%9E%8B%20any%EF%BC%8Cvoid%EF%BC%8Cunknown%EF%BC%8Cnever%E4%B9%8B%E9%97%B4%E7%9A%84%E5%8C%BA%E5%88%AB/">


<script id="page-configurations">
  // https://hexo.io/docs/variables.html
  CONFIG.page = {
    sidebar: "",
    isHome : false,
    isPost : true,
    lang   : 'zh-CN'
  };
</script>

  <title>TypeScript 中类型 any，void，unknown，never之间的区别 | hxy的博客</title>
  






  <noscript>
  <style>
  .use-motion .brand,
  .use-motion .menu-item,
  .sidebar-inner,
  .use-motion .post-block,
  .use-motion .pagination,
  .use-motion .comments,
  .use-motion .post-header,
  .use-motion .post-body,
  .use-motion .collection-header { opacity: initial; }

  .use-motion .site-title,
  .use-motion .site-subtitle {
    opacity: initial;
    top: initial;
  }

  .use-motion .logo-line-before i { left: initial; }
  .use-motion .logo-line-after i { right: initial; }
  </style>
</noscript>

<link rel="alternate" href="/atom.xml" title="hxy的博客" type="application/atom+xml">
</head>

<body itemscope itemtype="http://schema.org/WebPage">
  <div class="container use-motion">
    <div class="headband"></div>

    <header class="header" itemscope itemtype="http://schema.org/WPHeader">
      <div class="header-inner"><div class="site-brand-container">
  <div class="site-nav-toggle">
    <div class="toggle" aria-label="切换导航栏">
      <span class="toggle-line toggle-line-first"></span>
      <span class="toggle-line toggle-line-middle"></span>
      <span class="toggle-line toggle-line-last"></span>
    </div>
  </div>

  <div class="site-meta">

    <a href="/" class="brand" rel="start">
      <span class="logo-line-before"><i></i></span>
      <h1 class="site-title">hxy的博客</h1>
      <span class="logo-line-after"><i></i></span>
    </a>
      <p class="site-subtitle" itemprop="description">Mia san Mia!</p>
  </div>

  <div class="site-nav-right">
    <div class="toggle popup-trigger">
        <i class="fa fa-search fa-fw fa-lg"></i>
    </div>
  </div>
</div>




<nav class="site-nav">
  <ul id="menu" class="main-menu menu">
        <li class="menu-item menu-item-home">

    <a href="/" rel="section"><i class="fa fa-home fa-fw"></i>首页</a>

  </li>
        <li class="menu-item menu-item-about">

    <a href="/about/" rel="section"><i class="fa fa-user fa-fw"></i>关于</a>

  </li>
        <li class="menu-item menu-item-tags">

    <a href="/tags/" rel="section"><i class="fa fa-tags fa-fw"></i>标签</a>

  </li>
        <li class="menu-item menu-item-categories">

    <a href="/categories/" rel="section"><i class="fa fa-th fa-fw"></i>分类</a>

  </li>
        <li class="menu-item menu-item-archives">

    <a href="/archives/" rel="section"><i class="fa fa-archive fa-fw"></i>归档</a>

  </li>
      <li class="menu-item menu-item-search">
        <a role="button" class="popup-trigger"><i class="fa fa-search fa-fw"></i>搜索
        </a>
      </li>
  </ul>
</nav>



  <div class="search-pop-overlay">
    <div class="popup search-popup">
        <div class="search-header">
  <span class="search-icon">
    <i class="fa fa-search"></i>
  </span>
  <div class="search-input-container">
    <input autocomplete="off" autocapitalize="off"
           placeholder="搜索..." spellcheck="false"
           type="search" class="search-input">
  </div>
  <span class="popup-btn-close">
    <i class="fa fa-times-circle"></i>
  </span>
</div>
<div id="search-result">
  <div id="no-result">
    <i class="fa fa-spinner fa-pulse fa-5x fa-fw"></i>
  </div>
</div>

    </div>
  </div>

</div>
    </header>

    
  <div class="back-to-top">
    <i class="fa fa-arrow-up"></i>
    <span>0%</span>
  </div>
  <div class="reading-progress-bar"></div>

  <a href="https://github.com/huxingyi1997" class="github-corner" title="Follow me on GitHub" aria-label="Follow me on GitHub" rel="noopener" target="_blank"><svg width="80" height="80" viewBox="0 0 250 250" aria-hidden="true"><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" fill="currentColor" class="octo-body"></path></svg></a>


    <main class="main">
      <div class="main-inner">
        <div class="content-wrap">
          

          <div class="content post posts-expand">
            

    
  
  
  <article itemscope itemtype="http://schema.org/Article" class="post-block" lang="zh-CN">
    <link itemprop="mainEntityOfPage" href="https://hxy1997.xyz/2021/08/22/TypeScript%20%E4%B8%AD%E7%B1%BB%E5%9E%8B%20any%EF%BC%8Cvoid%EF%BC%8Cunknown%EF%BC%8Cnever%E4%B9%8B%E9%97%B4%E7%9A%84%E5%8C%BA%E5%88%AB/">

    <span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
      <meta itemprop="image" content="/images/Robben.gif">
      <meta itemprop="name" content="hxy">
      <meta itemprop="description" content="">
    </span>

    <span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
      <meta itemprop="name" content="hxy的博客">
    </span>
      <header class="post-header">
        <h1 class="post-title" itemprop="name headline">
          TypeScript 中类型 any，void，unknown，never之间的区别
        </h1>

        <div class="post-meta">
            <span class="post-meta-item">
              <span class="post-meta-item-icon">
                <i class="far fa-calendar"></i>
              </span>
              <span class="post-meta-item-text">发表于</span>
              

              <time title="创建时间：2021-08-22 00:00:00 / 修改时间：00:03:06" itemprop="dateCreated datePublished" datetime="2021-08-22T00:00:00+08:00">2021-08-22</time>
            </span>
            <span class="post-meta-item">
              <span class="post-meta-item-icon">
                <i class="far fa-folder"></i>
              </span>
              <span class="post-meta-item-text">分类于</span>
                <span itemprop="about" itemscope itemtype="http://schema.org/Thing">
                  <a href="/categories/web%E5%89%8D%E7%AB%AF/" itemprop="url" rel="index"><span itemprop="name">web前端</span></a>
                </span>
            </span>

          
            <span class="post-meta-item" title="热度" id="busuanzi_container_page_pv" style="display: none;">
              <span class="post-meta-item-icon">
                <i class="fa fa-eye"></i>
              </span>
              <span class="post-meta-item-text">热度：</span>
              <span id="busuanzi_value_page_pv"></span>
            </span>
  
  <span class="post-meta-item">
    
      <span class="post-meta-item-icon">
        <i class="far fa-comment"></i>
      </span>
      <span class="post-meta-item-text">Valine：</span>
    
    <a title="valine" href="/2021/08/22/TypeScript%20%E4%B8%AD%E7%B1%BB%E5%9E%8B%20any%EF%BC%8Cvoid%EF%BC%8Cunknown%EF%BC%8Cnever%E4%B9%8B%E9%97%B4%E7%9A%84%E5%8C%BA%E5%88%AB/#valine-comments" itemprop="discussionUrl">
      <span class="post-comments-count valine-comment-count" data-xid="/2021/08/22/TypeScript%20%E4%B8%AD%E7%B1%BB%E5%9E%8B%20any%EF%BC%8Cvoid%EF%BC%8Cunknown%EF%BC%8Cnever%E4%B9%8B%E9%97%B4%E7%9A%84%E5%8C%BA%E5%88%AB/" itemprop="commentCount"></span>
    </a>
  </span>
  
  

        </div>
      </header>

    
    
    
    <div class="post-body" itemprop="articleBody">

      
        <p>有点意思，转自<a target="_blank" rel="noopener" href="https://knightyun.github.io/2021/04/03/js-ts-type-compare">TypeScript 中类型 any，void，unknown，never之间的区别</a></p>
<span id="more"></span>

<p>TypeScript 拓展了 JavaScript 的基本类型与语言特性，为了覆盖类型检查的情景，衍生出了一些额外的类型，其中 <code>any</code>, <code>unknown</code>, <code>void</code>, <code>never</code> 这几个类型所适用的情形容易使人混淆，下面通过举例进行一下区分；</p>
<h2 id="any"><a href="#any" class="headerlink" title="any"></a>any</h2><p>这应该是 typescript 中最开始就会接触到的类型，顾名思义：<strong>任意类型</strong>，这也是 ts 中不写类型申明时的默认类型，即不作任何约束，编译时会跳过对其的类型检查，</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> val1: <span class="built_in">any</span>;</span><br><span class="line">val1 = <span class="string">&#x27;abc&#x27;</span>;</span><br><span class="line">val1 = <span class="number">123</span>;</span><br><span class="line">val1 = <span class="literal">true</span>;</span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> arry: <span class="built_in">any</span>[] = [<span class="number">123</span>, <span class="string">&#x27;abc&#x27;</span>, <span class="literal">true</span>, <span class="literal">null</span>];</span><br></pre></td></tr></table></figure>

<h2 id="void"><a href="#void" class="headerlink" title="void"></a>void</h2><p><code>void</code> 表示<strong>无任何类型</strong>，正好与 <code>any</code> 相反，没有类型，如果是函数则应没有返回值或者返回 <code>undefined</code>，和 C 等语言中的无返回值函数申明类似：</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">voidFn</span>(<span class="params"></span>): <span class="title">void</span> </span>&#123;&#125;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">voidFn1</span>(<span class="params"></span>): <span class="title">void</span> </span>&#123; <span class="keyword">return</span> <span class="literal">undefined</span>; &#125;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">voidFn2</span>(<span class="params"></span>): <span class="title">void</span> </span>&#123; <span class="keyword">return</span>; &#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">voidFn3</span>(<span class="params"></span>): <span class="title">void</span> </span>&#123; <span class="keyword">return</span> <span class="number">1</span>; &#125; <span class="comment">// Error</span></span><br></pre></td></tr></table></figure>

<p>变量也可以申明为 <code>void</code> 类型，只不过只能给这个变量分配 <code>undefined</code>, <code>null</code> 和 <code>void</code> 类型的值（如果 ts 配置文件中设置了 <code>&quot;strictNullChecks&quot;: false</code>，那么分配 <code>null</code> 类型的值也会报错）:</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> val1: <span class="built_in">void</span>;</span><br><span class="line"><span class="keyword">let</span> val2: <span class="literal">null</span> = <span class="literal">null</span>;</span><br><span class="line"><span class="keyword">let</span> val3: <span class="literal">undefined</span> = <span class="literal">undefined</span>;</span><br><span class="line"><span class="keyword">let</span> val4: <span class="built_in">void</span>;</span><br><span class="line"></span><br><span class="line">val1 = val2; <span class="comment">// &quot;strictNullChecks&quot;: false 时报错</span></span><br><span class="line">val1 = val3;</span><br><span class="line">val1 = val4;</span><br></pre></td></tr></table></figure>

<h2 id="unknown"><a href="#unknown" class="headerlink" title="unknown"></a>unknown</h2><p>顾名思义，<code>unknown</code> 表示<strong>未知类型</strong>，是 <code>typescript 3.0</code> 中引入的新类型，即写代码的时候还不清楚会得到怎样的数据类型，如服务器接口返回的数据，<code>JSON.parse()</code> 返回的结果等；该类型相当于 <code>any</code>，可以理解为官网指定的替代 <code>any</code> 类型的<strong>安全</strong>版本（因为不提倡直接使用 <code>any</code> 类型）；</p>
<p>它能被赋值为任何类型，但不能被赋值给除了 <code>any</code> 和 <code>unknown</code> 之外的其他类型，同时，不允许执行 <code>unknown</code> 类型变量的方法（<code>any</code> 可以），举个例子：</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> uk: unknown = <span class="string">&#x27;abc&#x27;</span>;</span><br><span class="line"></span><br><span class="line">uk = <span class="number">123</span>;</span><br><span class="line">uk = <span class="literal">true</span>;</span><br><span class="line">uk.toString(); <span class="comment">// Error</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> valAny: <span class="built_in">any</span> = <span class="string">&#x27;abc&#x27;</span>;</span><br><span class="line">valAny.toString(); <span class="comment">// &#x27;abc&#x27;</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> uk1: unknown = uk;</span><br><span class="line"><span class="keyword">let</span> uk2: <span class="built_in">any</span> = uk;</span><br><span class="line"><span class="keyword">let</span> uk2: <span class="built_in">string</span> = uk; <span class="comment">// Error</span></span><br></pre></td></tr></table></figure>

<h2 id="never"><a href="#never" class="headerlink" title="never"></a>never</h2><p><code>never</code> 同样顾名思义，表示<strong>永不存在的值</strong>的类型，是 <code>typescript 2.0</code> 中引入的新类型，概念有点绕，什么情况下变量会永远不存在值呢？因为通常情况下，变量一旦申明了，就会被分配值，即使没有特别指定，也会被初始化为 <code>undefined</code>，同样一个函数即使有个写返回值，也会默认返回 <code>undefined</code>，也不是真正的不存在返回值：</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> foo;</span><br><span class="line"><span class="built_in">console</span>.log(<span class="keyword">typeof</span> foo); <span class="comment">// &#x27;undefined&#x27;</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">bar</span>(<span class="params"></span>) </span>&#123;&#125;;</span><br><span class="line"><span class="built_in">console</span>.log(<span class="keyword">typeof</span> bar()); <span class="comment">// &#x27;undefined&#x27;</span></span><br></pre></td></tr></table></figure>

<p>其实确实有一些情形，值会永不存在，比如，从程序运行的维度讲，如果一个函数执行时抛出了<strong>异常</strong>，那么这个函数变永远不会有值了（因为抛出异常会直接中断程序运行，这样程序就运行不到返回值那一步了，即具有不可达的终点，也就永不存在返回了）：</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">err</span>(<span class="params">msg: <span class="built_in">string</span></span>): <span class="title">never</span> </span>&#123;</span><br><span class="line">    <span class="keyword">throw</span> <span class="keyword">new</span> <span class="built_in">Error</span>(msg);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">// 有机会到达终点的函数也算存在返回值，编译会报错</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">err1</span>(<span class="params"></span>): <span class="title">never</span> </span>&#123; <span class="comment">// Error</span></span><br><span class="line">  <span class="keyword">if</span> (<span class="built_in">Math</span>.random() &gt; <span class="number">0.5</span>) &#123;</span><br><span class="line">     <span class="keyword">throw</span> <span class="keyword">new</span> <span class="built_in">Error</span>(<span class="string">&#x27;message&#x27;</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>还有一种极端情况也比较类似，就是函数中执行无限循环的代码（<strong>死循环</strong>），这样也同样使得程序永远无法运行到函数返回值那一步，永不存在返回：</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">loopForever</span>(<span class="params"></span>): <span class="title">never</span> </span>&#123;</span><br><span class="line">    <span class="keyword">while</span> (<span class="literal">true</span>) &#123;&#125;;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>变量也可以直接申明为 <code>never</code> 类型，让它永不存在值，其实就是意思就是永远不能给它<strong>赋值</strong>，否则就会报错，这样就可以形成一种保护机制；</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> ne: <span class="built_in">never</span>;</span><br><span class="line"></span><br><span class="line">ne = <span class="number">123</span>; <span class="comment">// Error</span></span><br></pre></td></tr></table></figure>

<p>另外，<code>never</code> 是所有类型的子类型，意思就是它可以赋值给任何类型（前提是配置里 <code>&quot;strictNullChecks&quot;: false</code>，否则检查不通过）；</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> num: <span class="built_in">number</span> = <span class="number">123</span>;</span><br><span class="line"><span class="keyword">let</span> ne: <span class="built_in">never</span>;</span><br><span class="line"></span><br><span class="line">num = ne;</span><br></pre></td></tr></table></figure>

<p>同时也没有任何类型是 <code>never</code> 的子类型，除了 <code>never</code> 自身，即除了 <code>never</code> 任何类型都不能赋值给 <code>never</code> 类型的变量（如果前提是 <code>&quot;strictNullChecks&quot;: true</code>，<code>never</code> 也不能赋值给 <code>never</code>）；</p>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> ne1: <span class="built_in">never</span>;</span><br><span class="line"><span class="keyword">let</span> ne2: <span class="built_in">never</span>;</span><br><span class="line"></span><br><span class="line">ne1 = ne2;</span><br><span class="line"></span><br><span class="line"><span class="comment">// any 也不能分配给 never</span></span><br><span class="line"><span class="keyword">let</span> any1: <span class="built_in">any</span> = <span class="number">123</span>;</span><br><span class="line">ne1 = any1; <span class="comment">// Error</span></span><br></pre></td></tr></table></figure>
    </div>

    
    
    
      
<div>
        <div style="text-align:center;color: #ccc;font-size:14px;">-------------本文结束<i class="fa fa-paw"></i>感谢您的阅读-------------</div>
</div>
        

  <div class="followme">
    <p>欢迎关注我的其它发布渠道</p>

    <div class="social-list">

        <div class="social-item">
          <a target="_blank" class="social-link" href="/atom.xml">
            <span class="icon">
              <i class="fa fa-rss"></i>
            </span>

            <span class="label">RSS</span>
          </a>
        </div>
    </div>
  </div>


      <footer class="post-footer">
          <div class="post-tags">
              <a href="/tags/TypeScript/" rel="tag"><i class="fa fa-tag"></i> TypeScript</a>
              <a href="/tags/%E7%B1%BB%E5%9E%8B/" rel="tag"><i class="fa fa-tag"></i> 类型</a>
          </div>

        


        
    <div class="post-nav">
      <div class="post-nav-item">
    <a href="/2021/08/08/%E5%A6%82%E4%BD%95%E8%87%AA%E5%B7%B1%E5%AE%9E%E7%8E%B0%E4%B8%80%E4%B8%AA%E7%AE%80%E5%8D%95%E7%9A%84tree%20shaking/" rel="prev" title="如何自己实现一个简单的tree shaking">
      <i class="fa fa-chevron-left"></i> 如何自己实现一个简单的tree shaking
    </a></div>
      <div class="post-nav-item">
    <a href="/2021/08/28/TypeScript%E5%AE%9E%E7%94%A8%E7%B1%BB%E5%9E%8B/" rel="next" title="TypeScript实用类型">
      TypeScript实用类型 <i class="fa fa-chevron-right"></i>
    </a></div>
    </div>
      </footer>
    
  </article>
  
  
  



          </div>
          
    <div class="comments" id="valine-comments"></div>

<script>
  window.addEventListener('tabs:register', () => {
    let { activeClass } = CONFIG.comments;
    if (CONFIG.comments.storage) {
      activeClass = localStorage.getItem('comments_active') || activeClass;
    }
    if (activeClass) {
      let activeTab = document.querySelector(`a[href="#comment-${activeClass}"]`);
      if (activeTab) {
        activeTab.click();
      }
    }
  });
  if (CONFIG.comments.storage) {
    window.addEventListener('tabs:click', event => {
      if (!event.target.matches('.tabs-comment .tab-content .tab-pane')) return;
      let commentClass = event.target.classList[1];
      localStorage.setItem('comments_active', commentClass);
    });
  }
</script>

        </div>
          
  
  <div class="toggle sidebar-toggle">
    <span class="toggle-line toggle-line-first"></span>
    <span class="toggle-line toggle-line-middle"></span>
    <span class="toggle-line toggle-line-last"></span>
  </div>

  <aside class="sidebar">
    <div class="sidebar-inner">

      <ul class="sidebar-nav motion-element">
        <li class="sidebar-nav-toc">
          文章目录
        </li>
        <li class="sidebar-nav-overview">
          站点概览
        </li>
      </ul>

      <!--noindex-->
      <div class="post-toc-wrap sidebar-panel">
          <div class="post-toc motion-element"><ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#any"><span class="nav-text">any</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#void"><span class="nav-text">void</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#unknown"><span class="nav-text">unknown</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#never"><span class="nav-text">never</span></a></li></ol></div>
      </div>
      <!--/noindex-->

      <div class="site-overview-wrap sidebar-panel">
        <div class="site-author motion-element" itemprop="author" itemscope itemtype="http://schema.org/Person">
    <img class="site-author-image" itemprop="image" alt="hxy"
      src="/images/Robben.gif">
  <p class="site-author-name" itemprop="name">hxy</p>
  <div class="site-description" itemprop="description"></div>
</div>
<div class="site-state-wrap motion-element">
  <nav class="site-state">
      <div class="site-state-item site-state-posts">
          <a href="/archives/">
        
          <span class="site-state-item-count">80</span>
          <span class="site-state-item-name">日志</span>
        </a>
      </div>
      <div class="site-state-item site-state-categories">
            <a href="/categories/">
          
        <span class="site-state-item-count">8</span>
        <span class="site-state-item-name">分类</span></a>
      </div>
      <div class="site-state-item site-state-tags">
            <a href="/tags/">
          
        <span class="site-state-item-count">120</span>
        <span class="site-state-item-name">标签</span></a>
      </div>
  </nav>
</div>
  <div class="links-of-author motion-element">
      <span class="links-of-author-item">
        <a href="https://github.com/huxingyi1997" title="GitHub → https:&#x2F;&#x2F;github.com&#x2F;huxingyi1997" rel="noopener" target="_blank"><i class="fab fa-github fa-fw"></i>GitHub</a>
      </span>
      <span class="links-of-author-item">
        <a href="mailto:huxingyi1997@zju.edu.cn" title="E-Mail → mailto:huxingyi1997@zju.edu.cn" rel="noopener" target="_blank"><i class="fa fa-envelope fa-fw"></i>E-Mail</a>
      </span>
  </div>



      </div>

    </div>
  </aside>
  <div id="sidebar-dimmer"></div>


      </div>
    </main>

    <footer class="footer">
      <div class="footer-inner">
        

        

<div class="copyright">
  
  &copy; 
  <span itemprop="copyrightYear">2022</span>
  <span class="with-love">
    <i class="fa fa-frog"></i>
  </span>
  <span class="author" itemprop="copyrightHolder">hxy</span>
</div>

<div class="theme-info">
  <div class="powered-by"></div>
  <span class="post-count">博客全站共1039.2k字</span>
</div>

        
<div class="busuanzi-count">
  <script async src="https://busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script>
    <span class="post-meta-item" id="busuanzi_container_site_uv" style="display: none;">
      <span class="post-meta-item-icon">
        <i class="fa fa-user"></i>
      </span>
      <span class="site-uv" title="总访客量">
        <span id="busuanzi_value_site_uv"></span>
      </span>
    </span>
    <span class="post-meta-divider">|</span>
    <span class="post-meta-item" id="busuanzi_container_site_pv" style="display: none;">
      <span class="post-meta-item-icon">
        <i class="fa fa-eye"></i>
      </span>
      <span class="site-pv" title="总访问量">
        <span id="busuanzi_value_site_pv"></span>
      </span>
    </span>
</div>








      </div>
    </footer>
  </div>

  
  <script src="/lib/anime.min.js"></script>
  <script src="//cdn.jsdelivr.net/npm/lozad@1/dist/lozad.min.js"></script>
  <script src="/lib/velocity/velocity.min.js"></script>
  <script src="/lib/velocity/velocity.ui.min.js"></script>

<script src="/js/utils.js"></script>

<script src="/js/motion.js"></script>


<script src="/js/schemes/pisces.js"></script>


<script src="/js/next-boot.js"></script>




  




  
<script src="/js/local-search.js"></script>













  

  


<script>
NexT.utils.loadComments(document.querySelector('#valine-comments'), () => {
  NexT.utils.getScript('//unpkg.com/valine/dist/Valine.min.js', () => {
    var GUEST = ['nick', 'mail', 'link'];
    var guest = 'nick,mail,link';
    guest = guest.split(',').filter(item => {
      return GUEST.includes(item);
    });
    new Valine({
      el         : '#valine-comments',
      verify     : false,
      notify     : true,
      appId      : 'pQsO3ySbU4VtWN2j1FLA74Ha-gzGzoHsz',
      appKey     : 'QYacMDY2VY7Wazprg1X6FiUv',
      placeholder: "Just go go",
      avatar     : 'mm',
      meta       : guest,
      pageSize   : '10' || 10,
      visitor    : false,
      lang       : 'zh-cn' || 'zh-cn',
      path       : location.pathname,
      recordIP   : false,
      serverURLs : ''
    });
  }, window.Valine);
});
</script>

  
  <!-- 动态背景特效 -->
  <!-- 樱花特效 -->
    <script async src="/js/src/sakura.js"></script>
    <script async src="/js/src/fairyDustCursor.js"></script>
</body>
</html>
